Transistorized magneto ignition system for internal combustion engines

ABSTRACT

To control conduction of a semiconductor element, typically a transistor, in the primary circuit of an ignition coil, by rapidly blocking the conduction to generate a high voltage potential, a current sensitive element, typically a resistor of less than about one ohm is located in the primary circuit to provide a control signal depending on the current flowing through the primary, the resistor being connected in parallel with the control circuit of a switching transistor having its emittercollector path connected in parallel with the control circuit of the ignition transistor. Preferably, the ignition transistor is a composite Darlington-connected transistor pair.

United States Patent Haubner et al.

[451 July 15,1975

TRANSISTORIZED MAGNETO IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINESlnventors: Georg Haubner, Berg; Walter Hofer,

Schwabach; Peter Schmaldienst, Nurnberg, all of Germany Robert BoschG.m.b.H., Gerlingen, Schillerhohe, Germany Filed: Feb. 12, 1974 Appl.No.: 441,748

Assignee:

Foreign Application Priority Data Mar. 23, 1973 Germany 2314559 US. Cl.123/148 E; 315/209 Int. Cl. F02P 3/02 Field of Search 123/148 E, 148 CD,149 D;

References Cited UNITED STATES PATENTS Neapolitakis 310/70 R 3,435,2643/1969 Brand et al. 310/70 R 3,484,677 12/1969 Pitco 310/70 R 3,587,55211/1968 Varaut 123/148 E 3,605,713 9/1971 Le Master et a1 123/148 EPrimary ExaminerWendell E. Burns Assistant E.raminerJames W. Cranson,Jr. Attorney, Agent, or FirmFlynn & Frishauf [57] ABSTRACT To controlconduction of a semiconductor element, typically a transistor, in theprimary circuit of an ignition coil, by rapidly blocking the conductionto generate a high voltage potential, a current sensitive ele ment,typically a resistor of less than about one ohm is located in theprimary circuit to provide a control signal depending on the currentflowing through the primary, the resistor being connected in parallelwith the control circuit of a switching transistor having itsemitter-collector path connected in parallel with the control circuit ofthe ignition transistor. Preferably, the ignition transistor is acomposite Darlingtonconnected transistor pair.

18 Claims, 2 Drawing Figures TRANSISTORIZED MAGNETO IGNITION SYSTEM FORINTERNAL COMBUSTION ENGINES The present invention relates to asemiconductor controlled magneto ignition system for internal combustionengines. and more particularly to such a system in which a magnetoprovides ignition energy as well as control signals to provide a highvoltage pulse for the ignition spark. at a predetermined time.

Magneto ignition systems which are solid-state controlled havepreviously been proposed: usually. the primary circuit of a magnetoignition system is connected to the switching path of an electronicsemiconductor element which. at the proper instant. is controlled bymeans of a control signal to change from current conductive state toblocking state. Ignition coil operated systems function by opening theprimary circuit of the ignition system which, previously, was closed.The circuit element which opens the connection may be a breaker contact;in solid-state systems, an ignition transistor is usually used. Themagnetic field due to the primary current, when the ignition transistorwas in conductive state, then collapses and induces a high voltage pulsein the secondary winding, which is connected by means of the ignitioncable to a spark plug to provide the ignition spark. The ignitiontransistor can readily be controlled from conductive to blocking statein ignition systems where batteries are used to supply ignition power.since the requisite control voltages can be obtained from the terminalsof the battery. ln battery-less magneto ignition systems, however. astrong magnetic field must be generated in the ignition coil topractically short-circuit the primary current loop thereof, requiringsubstantial control voltages to change the ignition transistor fromconductive to blocking state. which substantial voltages must beobtained also from the magneto.

Control voltages to control the ignition transistor can be derived fromadditional pulse generators located in. or connected to the magnetosystem itself, which additional pulse generator provides the requisitecontrol signal to break the primary current circuit, at the properinstant of time. Such additional pulse generators are comparativelyexpensive and require additional space and components.

Transistorized magneto ignition systems have also been proposed in whicha resistor is connected in series to the ignition transistor. Acapacitor is connected in parallel to the resistor. When a positivevoltage half wave is sensed in the magneto armature, the ignitiontransistor is connected to be in conductive state, and the capacitor ischarged due to the voltage drop across the resistor, upon current flowin the primary circuit of the ignition system. The voltage on thecapacitor, at the proper ignition time, then controls a controltransistor to change to blocked state and, in turn, interrupts thecontrol circuit of the ignition transistor. The resistance in thecircuit which is necessary is in the order of from 2-4 ohms, in order toprovide sufficient control voltage to block the control transistor. Thisresistor, of this magnitude, then forms an undesired loading on theprimary circuit, resulting in a decrease in the amplitude of the primarycurrent, generating heat which must be removed, and limiting themagnetic field in the ignition coil during the positive half wave. Thehigh voltage pulse derived from the ignition coil then is limited, orthrottled, since a smaller magnetic field was initially present, so thatthe rate of change of the field will be less than that which can beobtained in the absence of the resistor.

It is an object of the present invention to provide a contactless(breakerless) solid-state magneto ignition system in which the level ofthe primary current to be interrupted at the ignition instant isessentially independent from the control circuit, and the elementsthereof connected in the primary current loop of the ignition circuit.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly. an element is locatedin the primary current loop or circuit of the ignition system whichprovides a control signal to a control switch, typically a switchingtransistor, which is so connected that its emittercollector path isconnected in parallel to the control curcuit or control path (forexample emitter-base) of the solid-state element. typically the ignitiontransistor. connected in the primary of the ignition circuit.

The invention will be described by way of example with reference to theaccompanying drawings. wherein:

FIG. 1 is a general schematic circuit diagram of an ignition system ofthe present invention, in which the control path. or control circuit ofthe solid-state switch in the primary current loop is bridged by acontrol transistor: and

FIG. 2 is a fragmentary illustration of a portion of a printed circuit,including part of the circuits of HG. I. when made in multi-chip form.

The ignition system 10 of FIG. 1 is designed for a single-cylinderinternal combustion engine. The ignition system 10 has a rotating systemof magnets 11, on which a plurality of uniformly distributed.alternately poled magnets 12 are placedThese magnets may. for example.be secured to the flywheel of the internal combustion engine (not shown)and be driven thereby. They cooperate with an ignition armature 13,located on the housing of the internal combustion engine. The armature13 has windings 14 thereon. The windings 14 are split into a primary14a. and .a secondary 14b. The secondary 14b is connected over anignition cable 15 with the spark plug 16. The primary 14a of theignition armature 13 is connected to a primary circuit which includes atransistor unit 17., connected as a pair of transistors 25, 26 in aDarlington circuit. One terminal of the primary 140. as well as of thesecondary 14b and of the spark plug 16 is connected to chassis orground. forming a chassis bus 24. The other terminal of the primaryignition coil 14a is connected to a primary ignition circuit connection18 which connects to the electronics 19 of the ignition system. Theconnection 18 has two series connected diodes 20, 21 in series with thecollector terminal of the transistor unit 17. The base of the transistorunit 17 is connected over a resistor 22 with the anode of diode 20, andhence with line 18, and to the terminal of the primary winding 14a ofthe armature 13 which is not connected to chassis.

The primary circuit of the ignition system further includes a circuitelement which provides a control signal which varies in dependence onthe current flowing in the primary circuit. This element is a low-ohmicresistor 23. Preferably it is in the order of about 0.5 ohm. The voltageacross this small resistance provides a control signal when the primarycurrent in the primary circuit loop which includes primary coil 14a hasreached a certain value which is at the maximum, or close to the maximumof the current flow therein. The control resistor 23 is connected inseries with the switching path. that is, the emitter-collector path ofthe main transistor of the Darlington unit 17. The Darlington unit 17itself includes an npn ignition transistor 25, the emittercollector pathof which is directly connected in the ignition loop, and a controltransistor 26, the collector of which is connected to the collector ofthe transistor 25, and the emitter of which is connected to the base ofthe transistor 25. The control circuit of the transistor unit 17 is thusformed by the base of the auxiliary transistor 26 and the emitter of theignition transistor 25. A switching npn transistor 27 has itsemittercollector path connected in parallel to the circuit formed by thecontrol circuit of the unit 17, in series with the resistor 23. The baseof the switching transis tor 27 is connected to the free terminal of theresistor 23, that is, to the terminal which is not connected to chassisbut rather to the emitter of the transistor 25 of unit 17. A forwardlypolarized diode 28 and a resistor 29 connect the base of the switchingtransistor 27 to the junction between resistor 23 and the Darlingtonunit 17. The base of the switching transistor 27 further is connected tothe tap point of a voltage divider formed of resistors 30, 31 andconnected across buses 18, 24. that is, in parallel to the primary coil14a. The negative voltage half wave in the primary circuit of the systemis bridged by a diode 32, in series with a resistor 33, and connected tobe forwardly polarized with respect to the negative half wave.

Operation: Upon starting of the internal combustion engine, the magnetsystem 11 is rotated in the direction of the arrow. so that thepermanent magnets 12 provide a change of magnetic flux in the armature13, which therefore generates sequential positive and negative halfwaves. A positive half wave sensed in the primary winding 14a istransmitted over resistor 22 to the base of the Darlington transistorunit 17. The emitter of the unit 17 is connected to chassis over theresistor 23. As the voltage in the primary circuit rises, base currentbegins to flow which switches the transistor unit 17 into conductivestate, since the unit 17 is connected to the chassis bus 24 over theresistor 23. The primary circuit is now closed over the diodes 20, 21,the emittercollector (or main current) path of the ignition transistor25 of unit 17, and the resistor 23. The voltage drop in the diodes 20,21 which arises is merely that which is necessary to hold the transistorunit 17 in conductive state.iThe primary circuit is, practically,short-circuited and the current may rise to its maximum value which, inan example, is about 3A. The ignition armature current will provide asubstantial armature reaction, however, causing the primary voltage tobe sharply attenuated.

The voltage drop across the resistor 23 is connected over resistor 29and diode 28 to the base of the switching transistor 27. When theprimary current reaches a predetermined value, for example about 3A.transistor 27 responds, that is, the threshold level of the switchingtransistor 27 is exceeded and it begins to become conductive. Theswitching path of the switching transistor 27 is connected parallel tothe control circuit of the transistor unit 17. Thus, the base current ofthe transistor unit 17 is increasingly short-circuited over the maincurrent (emitter-collector) path of the switching transistor 27, so thatless base current can be applied to the unit 17 which quickly willcontrol the switching transistor 25 to change into blocked condition. Assoon as the primary current decreases, primary voltage rises immediatelyand is transferred over resistors 30, 31 to the base of the switchingtransistor 27. As the voltage on ,the base of the switching transistor27 rises, the transistor 27 quickly becomes conductive. In actualpractice, transistor 27 will rapidly switch over to conductive state,which completely short-circuits the control path of the transistor unit17, so that switching transistor 25 will block and the main switchingpath (emittercollector) of the ignition transistor will abruptly andcompletely block and effectively become an open circuit. Thissubstantial change in current flow occurring rapidly in the primary ofthe armature 13 provides a substantial change in field which istransformed by secondary 14b to a high voltage pulse which'results in anignition pulse and hence a spark at spark plug 16. The positive voltageplus arising in the primary 14a is not applied to the transistor 17,since the voltage divider 30, 31 has controlled transistor 27 to beconductive, thus effectively short-circuiting the control circuit, orcontrol path of the transistor unit 17.

As the positive voltage half wave in the primary circuit decreases, theresponse level of the base of the switching transistor 27 will be passedin a negative direction, and switching transistor 27 will again block.This-terminates bridging, or short-circuiting of the control path of thetransistor unit 17. The subsequent negative voltage half wave isbypassed by diode 32 and resistor 33, which provide a load on thearmature during the half wave of such extent that high voltages whichmight cause a misfire, or a stray pulse in the secondary winding 14b ofthe armature 13 are effectively suppressed.

The electronics 19 can be made as a single compact, replaceable unit, asseen in FIG. 2. An insulating carrier plate 41 is embedded in a pottingcompound 40, the carrier plate 41 carrying a printed circuit. Pottingcompound 40 is partly broken away to illustrate conductor strips 42, theresistor 23, as well as the transistor unit 17 and a diode unit 43including diodes 20, 21. The diode unit 43, comprising the two diodes20, 21, and the transistor unit 17 may be separate discrete componentshaving connecting tabs 44, 44' to form connections for the printedcircuit conductors 42, and connecting strips 42, to permit soldering orotherwise connection in a single integrated printed circuit unit. Theresistor 23 is part of the printed circuit. It may be a thick-filmelement, or may be a thin-film element, depending on the method to makethe printed circuit. The resistor 23 preferably is so constructed thatits resistance value can be changed by removing indentations 45therefrom, of greater or lesser extent, for example by removal ofmaterial by means of sand blasting, a laser beam, or the like.

Various changes and modifications may be made. The resistor 23 may, forexample, be made from doped semiconductor material, which can becombined with further electronic elements of the ignition system in asingle integrated circuit. This is a desirable alternative, since thetemperature-dependent changes in resistance in the controlcircuit of theswitching transistor 27 are thus effectively compensated.Temperature-dependent changes in resistance might otherwise result inundesirable change in theignition timing, that is, in the instant atwhich ignition occurs with respect to the specific rotary position ofthe engine, and hence the magnetic system ll. Forming resistor 23 as asemiconductor elecombustion engine is a premium. A separate ignitioncoil is then needed. theprimary winding of which is connected in circuitwith the armature. The transistor unit 17 and the switching transistor27 may also be replaced by various other electronic elements-or systems.The necessary feature of the present invention. that is. switching aswitching transistor in dependence on a control signal derived from theprimary current must be maintained, the switching transistor having itsmain current path connected in parallel to the control path of the maincontrolling semiconductor element. that is. the element corresponding totransistor unit 17 in the primary current circuit or loop of theignition system.

Various other changes and modifications may be made within the scope ofthe inventive concept.

We claim:

1. Magneto ignition system for internal combustion engine havingrotating magnet means and a primary winding coupled thereto to generatedelectrical ignition energy therein; a secondary winding connected to theprimary winding to generate ignition spark energy. for connection to aspark plug of the internal combustion engine; and an ignition controlcircuit connected to the primary winding comprising switchingsemiconductor means (17; 25, 26) having its main current-carrying pathconnected in series with the primary windins (140);

a controlled switching semiconductor (27) having its maincurrent-carrying path connected in parallel to the circuit including thecontrol electrode of the switching semiconductor means (17) to bypasscurrent therethrough;

and means (23) sensing current flow through the primary winding, saidcurrent flow sensing means (23) being connected to the control electrodeof said switching semiconductor means (17; 25, 26). to control theswitching semiconductor means (17; 25, 26) by said sensing means (23) tobecome conductive when the sensing means senses current flowing at apredetermined level in the primary winding and through the switchingsemiconductor means.

2. System according to claim 1, wherein the switching semiconductormeans (17; 25; 26) and the controlled switching semiconductor (27) bothcomprise a transistor.

3. System according to claim 2, wherein the control transistor (27) andthe current sensing means (23) are relatively arranged and connectedsuch that the control transistor becomes conductive at, or just belowthe maximum current flow through the main current path of the switchingtransistor means (17).

4. System according to claim 2, wherein the sensing means comprises aresistor of up to about 1 ohm resistance. the voltage drop across theresistor forming a sensing signal connected to and controlling thecontrol electrode of said control transistor (27).

5. System according to claim 4, wherein the resistance of said resistoris in the order of about V2 ohm.

6. System according to claim 2, wherein the switching transistor meanscomprises a transistor unit con nected in aDarlington circuit.

-7. System according to claim 6, wherein the sensing means comprises aresistor in the order of up to about 1 ohm resistance. connected tochassis of thesystem with one terminal and to the Darlington-conne ctedtransistor unit with the other terminal.

8. System according to claim 2, wherein the control switching transistor(27) has its base connected to the sensing means. said sensing meanscomprising a resistor connected to chassis with one terminal. and to thebase of the control transistor with the other terminal.

9. System according to claim 8, further comprising a diode (28)connected between the base of the control transistor (27) and the otherterminal of the resistor (23). the diode being poled in conductivedirection from the resistor (23) to the control transistor base.

10. System according to claim 8, further comprising a resistor (29)connected between the base of the control transistor (27) and the otherterminal of the resistor (23) forming the sensing means.

11. System according to claim 9, further comprising a resistor (29)connected in series with the diode (28 12. System according to claim 8,further comprising a voltage divider (30, 31) connected across theprimary winding (14a) and in parallel thereto. the tap point of thevoltage divider being connected to the base of the control transistor(27).

13. System according to claim 2, wherein the sensing means (23)comprises temperature responsive resistance means having a temperaturecoefficient which matches the temperature coefficient of the controltransistor (27) to compensate temperature effects in the system.

14. System according to claim 1, wherein the sensing means comprisesresistance means (23) which includes doped semiconductor material,having a resistance in the other of up to about 1 ohm.

15. System according to claim 14, wherein the control resistor (23)comprises a plurality of pn junctions.

16. System according to claim 1, wherein the sensing means comprises aresistor in the order of up to about 1 ohm formed as part of a printedcircuit as a resistor film.

17. System according to claim 15, wherein the resistor is formed as aresistor mass on the printed circuit, the resistance of which isadjusted by removing portions of said resistance mass.

18. System according to claim 14, wherein the doped semiconductormaterial, and at least the switching semiconductor means form part of anintegrated circult.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENTNO. 3,89 ,525

DATED July 15, 1975 INVENTUMS): Georg HAUBNER et al It is certified thaterror appears in the above-identified patent and that said LettersPatent is hereby corrected asshown below:

Claim 1 Column 5, lines 48, 4 9 change uconfductiveuto --non con-ductiver I a Signed and Sealed This Fourth Day of November, 1986 [SEAL] Arrest:

DONALD J. QUIGG Arresting Ojficer Commissioner of Parents and Trademarks

1. Magneto ignition system for internal combustion engine havingrotating magnet means and a primary winding coupled thereto to generatedelectrical ignition energy therein; a secondary winding connected to theprimary winding to generate ignition spark energy, for connection to aspark plug of the internal combustion engine; and an ignition controlcircuit connected to the primary winding comprising switchingsemiconductor means (17; 25, 26) having its main current-carrying pathconnected in series with the primary windins (14a); a controlledswitching semiconductor (27) having its main current-carrying pathconnected in parallel to the circuit including the control electrode ofthe switching semiconductor means (17) to bypass current therethrough;and means (23) sensing current flow through the primary winding, saidcurrent flow sensing means (23) being connected to the control electrodeof said switching semiconductor means (17; 25, 26), to control theswitching semiconductor means (17; 25, 26) by said sensing means (23) tobecome conductive when the sensing means senses current flowing at apredetermined level in the primary winding and through the switchingsemiconductor means.
 2. System according to claim 1, wherein theswitching semiconductor means (17; 25; 26) and the controlled switchingsemiconductor (27) both comprise a transistor.
 3. System according toclaim 2, wherein the control transistor (27) and the current sensingmeans (23) are relatively arranged and connected such that the controltransistor becomes conductive at, or just below the maximum current flowthrough the main current path of the switching transistor means (17). 4.System according to claim 2, wherein the sensing means comprises aresistor of up to about 1 ohm resistance, the voltage drop across theresistor forming a sensing signal connected to and controlling thecontrol electrode of said control transistor (27).
 5. System accordingto claim 4, wherein the resistance of said resistor is in the order ofabout 1/2 ohm.
 6. System according to claim 2, wherein the switchingtransistor means comprises a transistor unit connected in a Darlingtoncircuit.
 7. System according to claim 6, wherein the sensing meanscomprises a resistor in the order of up to about 1 ohm resistance,connected to chassis of the system with one terminal and to theDarlington-connected transistor unit with the other terminal.
 8. Systemaccording to claim 2, wherein the control switching transistor (27) hasits base connected to the sensing means, said sensing means comprising aresistor connected to chassis with one terminal, and to the base of thecontrol transistor with the other terminal.
 9. System according to claim8, further comprising a diode (28) connected between the base of thecontrol transistor (27) and the other terminal of the resistor (23), thediode being poled in conductive direction from the resistor (23) to theControl transistor base.
 10. System according to claim 8, furthercomprising a resistor (29) connected between the base of the controltransistor (27) and the other terminal of the resistor (23) forming thesensing means.
 11. System according to claim 9, further comprising aresistor (29) connected in series with the diode (28).
 12. Systemaccording to claim 8, further comprising a voltage divider (30, 31)connected across the primary winding (14a) and in parallel thereto, thetap point of the voltage divider being connected to the base of thecontrol transistor (27).
 13. System according to claim 2, wherein thesensing means (23) comprises temperature responsive resistance meanshaving a temperature coefficient which matches the temperaturecoefficient of the control transistor (27) to compensate temperatureeffects in the system.
 14. System according to claim 1, wherein thesensing means comprises resistance means (23) which includes dopedsemiconductor material, having a resistance in the other of up to about1 ohm.
 15. System according to claim 14, wherein the control resistor(23) comprises a plurality of pn - junctions.
 16. System according toclaim 1, wherein the sensing means comprises a resistor in the order ofup to about 1 ohm formed as part of a printed circuit as a resistorfilm.
 17. System according to claim 15, wherein the resistor is formedas a resistor mass on the printed circuit, the resistance of which isadjusted by removing portions of said resistance mass.
 18. Systemaccording to claim 14, wherein the doped semiconductor material, and atleast the switching semiconductor means form part of an integratedcircuit.